I'll generally play a couple of hours every day while my missis watches the soaps! If I have a day off work in the week i'll play longer, maybe 6 or 7 hours in some deep stacks or just grinding the low SnG's.
I stick to one room through a day though, either Stars or Tilt, unless there is something in particular I wanna play in on Party Poker
I dont think 2/3 hours is unhealthy, long as your not neglecting work or family. There's got to be a good balance.
My girlfriend went to London for a hen night a few weeks ago and I played for 12 hours straight only stopping to make a pizza. Lol, those days are VEY few and far between though, I have the utmost respect for the guys who grind that much daily!